Investigation On Laser-MAG Hybrid Backing Weld And Twin-wire MAG Cosmetic Welding Process For Core Pan

The scraper conveyor for coal and metal mining is one of China’s pivotal developing research of 10 sectors,the core pan,as the main welding structure of the scraper conveyor,its welding quality and service life related to the whole equipment’s runing.Currently,the traditional MAG manual welding method is widly used for the core pan welding,manual arc welding is a low efficiency welding method,and the welding process is difficult to control and poor technical difficulties on adaptability. In this paper,the thickness of 45 mm core pan NM400 and casting ledge ZG30 Si Mn dissimilar steels’ s welding was studied,the technology research of laser-MAG hybrid welding heat for backing weld,twin-wire MAG heat for filling and cosmetic welding were carried out. The incomplete penetration of backing weld and the study of cold cracks and hot cracks and other problems were focused on.The effects of heat input,the form of groove joint and the welding materials matching on the welding quality and conventional mechanical properties,considerated the stretch strength, microhardness,microstructure and impact energy as the evaluation indexs,and ultimately achieved the automation welding process for large scraper conveyor core pan.The effects of laser power,the defocus amount,weaving amplitude and weaving frequency and other basic process parameters on the welded joint were investigated,and the advantages of laser-MAG hybrid welding heat backing weld in the core pan were analyzed,and ultimately accessed the optimum parameters for the core pan welding. The results showed that for different slope forms,to ensure the penetration of the premise,a small laser power,positive defocus proper and the beam weaving appropriately can be effectively suppress the weld porosity and incomplete fusion and other fusion defects. And the laser hybrid welding process had a good condition adaptability,respectively,when the welding gap was 0~2mm, the wrong side was 0~2mm,the blunt edge size was 2~6mm to simulate conditions in the area had been backing weld good side welding molding. Twin-wire MAG heat for filling and cosmetic welding,when the beam weave appropriately,weaving frequency was 20 Hz,weaving amplitude was 1 ~ 2mm,can inhibit the lack of fusion,slag and other welding defects.The effective measures were abtained to curb the cold cracking for backing weld of the core pan weld,which used the laser-MAG hybrid welding method and made a preheat,through straight Y-groove cold cracking susceptibility test proposed the preheat temperature of two kinds of ER69-G and ER50-6 respectively,the required critical preheat temperature for welding materials is 100℃and 70℃ respectively,When the intensity of welding material was lower,the preheat temperature was lower;Conversely,it was higher.For the hot cracking for backing weld of the core pan welded joint,laser-MAG arc hybrid welding method was taken,through the macro and micromorphology analysis methods,scanning fracture morphology and EDS ingredients and other analytical tools were taken to identify as solidification cracking,and analyzed the impacts of the chemical composition of the weld and welding groove forms on solidification cracking,laser-MAG hybrid welding method was used to inhibit solidification cracking,combined the methods of lowering the base metal dilution rate and reducing joint stress concentration.Based on the study of welding process to obtain a good welded joint,the effects of the heat input,the welding materials in the form of groove matching on the joint microstructure and hardness,tensile,impact energy and other mechanical properties were discussed respectively,The study found that,when the heat input increased,the martensite transformation to bainite of the welded joint and the strength of joint decreased significantly,when the heat input is of 10 ~ 15 k J/cm,the lath martensite and bainite were staggered distribution,the best mechanical properties of joint were abtanied;the mechanical properties of joint roots for the double semi-U-groove and double U-groove were better than double V-groove,but the mechanical properties of the upper joint for three grooves were similar,for the mechanical properties of the entire welded joint,double U and double semi-U-groove were better;Make a comparison of different welding material matching,drew that the ladder matching form of low intensity(ER50-6) for backing welding,high-strength(ER69-G) for cosmetic welding was good,both ensured the joint root welding quality and got a good joint mechanical properties,and reduced the preheat temperature.